The Somerset Raritan Valley Sewerage Authority has raised concerns over the state methodology in measuring sewer flows. Above is a July 2007 file photo of a Metuchen Sewer Department employee looking in a manhole during a water main break.Joe Epstein/The Star-Ledger

BRIDGEWATER — When it comes to measuring future sewer service needs, several Somerset County municipalities want state officials to pay closer attention to the weather.

Given how weather conditions can impact sewer flows, the Somerset Raritan Valley Sewerage Authority has raised concerns about state regulations that would mean using a recent dry spell to measure existing flows and ultimately determine future needed capacity.

That scenario provides an unrealistically low estimate of existing sewer flows and could impede the authority in providing sewer treatment for future economic growth, officials said.

“We work for the public…and we should get it right,” said Glen Petrauski, the authority’s executive director. “It’s a matter of getting the right number.”

In order to account for wet and dry cycles, authority and Somerset County officials have called on the state Department of Environmental Protection to accept an alternate methodology in measuring existing flows at the authority’s Bridgewater plant.

That alternative would allow the authority to handle larger flows during severe wet weather and also better accommodate redevelopment and future growth, said Laurette Kratina, a supervising planner with the county planning department.

The dispute centers on state regulations for countywide wastewater management plans, which require that existing flows represent the monthly average of the most recent 12 months. Those existing flows are then combined with anticipated flows from future growth to determine future capacity needs.

New Jersey Department of Environmental Protection Commissioner Bob Martin speaks during a May event in Mantoloking.Tony Kurdzuk/The Star-Ledger

DEP officials have previously said that methodology is “most appropriate because it reflects the most current wastewater contributions.”

“By using a full annual cycle, seasonal changes due to population or rainfall/ground water level fluctuations will generally be captured in establishing the existing wastewater flows,” the department said.

In developing its plan, Somerset County has been using the timeframe of April 2012 to March 2013, the most recent data available when the analyses began.

Since that 12-month period was particularly dry, officials argue that the estimate presents an inaccurate snapshot of existing flows and would unjustly reduce the authority’s future capacity. Since rainfall can infiltrate the system, there is greater flow under wet conditions and less flow at dry times, officials said.

“It’s just unrealistically low,” said Kratina, referring to the estimate of existing flows.

As an alternative, authority and county officials have proposed measuring existing flows by the highest 12-month rolling average over the last five years. The county also has recommended that the same methodology be used for Montgomery Township.

For the authority, that alternative would mean a future capacity of about 28 million gallons per day, compared with roughly 21 million gallons under the state’s methodology, officials said.

If future capacity was connected to that dry spell and the authority sought to exceed that level to accommodate future growth, officials would have to amend the wastewater management plan, which could take years to accomplish, Petrauski said.

“What happens to that development?” he said. “It’s gone.”

In fact, the future capacity linked to that dry period – after factoring in future development – would be less than flows already seen by the authority in the past, according to James Cosgrove, Jr., an environmental engineer and a consultant to the authority.

“You’re guaranteeing yourself that you’re getting the wrong answer, because you’re getting a number that is less than what (has) actually already been experienced,” Cosgrove said. “It makes no sense.”